An aluminum sheet undergoing electrochemical anodization may form aluminum oxide having a hexagonal array of vertical nanopores defined therein. For this process, the relationship between the anodization potential, the pore diameter and the interpore distance has been investigated. See, Rao, Y. L. et al., J. Nanosci. Nanotech., 2, 12, 2070-2075 (2005). It has been determined that the pore diameter (PD) may be related to the anodization potential (AP) by Formula I:PD=1.35 (nm/V)*AP(V)  (I).
It has also been determined that the pore spacing (PS, or interpore distance) may be related to the anodization potential by Formula II:PS=2.58 (nm/V)*AP(V)  (II).
Thus, in theory, in a spontaneous pore-forming process, the pore diameter and interpore distance of the nanopores can be set by adjusting the anodization potential according to these formulas. However, a spontaneous pore-forming process may not lead to a pore distribution pattern that is perfectly hexagonal due to inherent atomic defects in the aluminum. Therefore, if a conductive material is deposited into such nanopores and the aluminum oxide is removed, the resulting nanopillars may also not be in a mono-domain hexagonal array. As such, new methods of forming hexagonal arrays of nanopores and new methods of forming conductive nanopillars therefrom, particularly conductive nanopillars having large interpillar distances, may be needed.